In the selective separation of mineral phases by flotation, surface chemistry is the principal determinant of the average contact angle for a specific mineral phase in a flotation pulp. The average contact angle is, in turn, the principal determinant of the bubble-particle attachment efficiency (Ea) in the overall collection efficiency (Ec) from which the flotation rate constant can be determined (Ralston 1994). The recovery and selectivity in sulfide flotation is ultimately dependent on the relative rate constants of the different mineral phases. But the average contact angle is not only mineral-specific, based on a statistical average of the mineral particles in that phase, but also the contact angle for each particle is an average of hydrophobic and hydrophilic areas across the particle surface. Determination of this hydrophobic/hydrophilic balance by particle therefore requires selection of the particular mineral phase and statistical analysis of the particles with an estimation of the spread of values. In a flotation pulp containing many different mineral phases, different particle sizes of individual phases, adsorbed and precipitated species (often colloidal), and oxidised products, this is not a simple task.
The hydrophobic/hydrophilic balance by particle and its statistical average by mineral phase requires identification of the major species contributing to each category in surface layers (Smart 2003a). In addition to adsorbed collector molecules and their oxidised products (e.g. dimers), hydrophobicity can be imparted to sulfide mineral surfaces by oxidation to produce polysulfide Sn2− species resulting from loss of metal ions (usually Fe2+) from surface layers. In acid solution, hydrophobic elemental sulfur can also be formed usually imaged in patches on the sulfide mineral surface (Smart et al. 2003b). Almost all other species found on sulfide mineral surfaces, such as oxide/oxyhydroxide/hydroxides, oxy-sulfur (e.g. sulfate), carbonate, hydrous silica and fine gangue particles, are essentially hydrophilic but may be in the form of localised particles, colloids and precipitates or continuous, reacted or precipitated surface layers (Smart et al. 2003b).
The action of collector molecules in inducing hydrophobicity can be assisted by activating species such as copper and lead ions that complex the collector on the surface. Previous research has shown that this activation can be inadvertently produced by dissolution and transfer via solution of these ions to mineral phases not intended to float (Smart 1991; Lascelles & Finch 2002; Finkelstein 1997). The mechanisms of activation of sphalerite (Gerson et al. 1999) and pyrite (Weisener & Gerson, 2000) by copper have been elucidated.
Hence, there is a need to find more reliable methods of mineral phase recognition in these complex surface chemistries and therefore, it would be very advantageous to provide a method which overcomes the aforementioned difficulties.